The goal of this research is development and testing of a new type of shaped field collimator system to mount on existing oncology therapy linear accelerators and cobalt units. The collimator allows the radiation beam to be shaped in arbitrary irregular patterns to match the size and shape of the tumor so that dose to the tumor region will be maximized relative to the dose received by surrounding normal tissue. The shaping of the radiation field is by an array of movable but permanently mounted tungsten rods, the position of the rods being set automatically by easy-to- fabricate styrofoam patterns. Medical technicians are relieved of the burden (and of the frequent minor injuries) associated with handling of cast heavy metal collimators which are at present in frequent use for shaping of irregular fields. The new "rod-type" collimator will reduce operating costs, improve staff moral by making their job easier, and increase the number of patients which a facility can handle. The research plan involves collecting data on collimator attachment arrangements for 4 to 6 of the most frequently used therapy devices, designing collimators for these devices, performing life-cycle tests on critical elements, and upgrading and existing prototype to fully automated status and installing this prototype for weekend debugging periods on an existing therapy unit.